[Feature] #8 - Past era reports

[kukabi]

User story

As a user, I want to be able to view detailed information about a past era so that I can have comparative insight about my validator and other validators, and plan for the future.

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Feature Details

Data that can be viewed for a selected era:

• Total reward.
• Era active validators.
• Total reward points and rewards distributed.
• Reward per validator.
• Nominator details per validator.
• Blocks produced per validator.

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Implementation Details:

This data is served from the indexed SubVT database.